In the thesis, I discussed the economic thermal insulation thickness on the outer wall and under the base plate. I also compared the prices of constructing a classically built and prefabricated house. In the first part, I presented characteristics of the classically built and the prefabricated house and defined the theoretical bases of energy efficiency. In the second part, I described the chosen object and prepared an inventory of the material for the cases of a classically built house and a prefabricated one, where I compared the prefabricated house by Marles with the N14 composition of the outer wall. Based on the chosen object I calculated the economic thermal insulation thickness of the outer walls for a period of 60 years, where the façade is being renovated twice, and the economic thermal insulation thickness under the base plate with the assumed lifetime of 100 years for the case of a classically built house. I also considered the possibility of no thermal insulation under the base plate. For the calculation, I used the dynamic method, used in economics, called net present value. In continuation I prepared an inventory of the work and material for the construction of the chosen object and so compared the prices for the construction of a classically build and a prefabricated house. For the purpose of comparability, I unified some elements of the classically built house with the offer for the prefabricated house Marles Mega N14, so that both objects are the same in terms of energy efficiency and equipment. In the thesis, I showed that the installation of large amounts of thermal insulation pays off at the outer walls as well as under the base plate. The results of the price comparison for the classically built house and the prefabricated one showed that the construction of a classically built object is still cheaper for about 20%.